1. Field of the Invention
This invention relates to a method of recording information and an information recording medium which can be used in carrying out the method, and more particularly to a method of recording information on an information recording medium, comprising a semiconductor layer and a ferroelectric layer formed thereon, by the use of polarization in the ferroelectric layer.
2. Description of the Prior Art
As an information recording medium for recording an image signal, a sound signal or the like or for use as a data memory for computers, there have been known mediums in which information is recorded in the form of unevenness, such as pits, and is reproduced by detecting the change in the electrostatic capacitance caused by the uneveness. See, for instance, Japanese Unexamined Patent Publication No. 47(1972)-37403.
Further as an information recording medium on which information can be recorded in a very high density while permitting reproduction and erasure of the information, there have been known those which comprises a semiconductor layer and a ferroelectric layer formed thereon and on which information is recorded in the form of directions of polarization in the ferroelectric layer. See, for instance, Japanese Unexamined Patent Publication No. 57(1982)-27447. Further, a method of and an apparatus for recording information on such information recording medium have been known. In the method or the apparatus, information is recorded by applying electric voltages modulated according the information to the ferroelectric layer while moving a conductive head along the ferroelectric layer and selectively polarizing only predetermined parts of the ferroelectric layer in predetermined directions. Further there has been proposed a method of reproducing the information recorded thereon by detecting the change in the electrostatic capacitance caused by depletion layer formed by the polarization of the ferroelectric layer.
In the method described above where polarization of the ferroelectric layer is used for recording, an electric field which is formed in the ferroelectric layer by applying a predetermined electric voltage between the conductive head and the semiconductor layer or by electrifying the surface of the ferroelectric layer by charged particles from the conductive head polarizes the ferroelectric layer in the normal direction of the ferroelectric layer thereof, and a depletion layer is formed in the semiconductor layer adjacent to the ferroelectric layer according to the direction of polarization, whereby recording is effected. The degree of polarization of the ferroelectric layer depends upon the time for which the electric field is applied to the ferroelectric layer. Accordingly when the conductive head passes a desired recording region before completion of polarization of the ferroelectric layer, the electric field established by the voltage between the conductive head and the semiconductor layer is naturally removed, and at the same time the charge on the surface of the ferroelectric layer is generally immediately dispersed, which results in incompletion of polarization and readout errors in reproduction of the information. Accordingly, the conductive head must be moved slowly so that a given recording region is completely polarized. The time required for polarization is markedly long as compared with the data transfer time required for application of electric voltages (modulated according to information data) to the information recording medium, and the polarization speed governs the information recording speed and prevents shortening of the recording time.